A. Field of the Invention
The present invention relates to an impact tool for driving fasteners into a workpiece.
B. Description of the Prior Art
In industries such as the construction industry, impact tools are employed to drive fasteners into a workpiece. For example, these tools may be used to drive a nail into a stud to secure wallboard. A tool of this type may be pneumatically powered. Such a tool, however, requires a source of high pressure air or similar fluid. This limits the tool's utility, since the tool may only be used within a reasonable distance of a source of pressurized air such as a compressor.
A more readily available source of power is electricity. Consequently, many impact tools are electrically operated thereby increasing their convenience to the user. In order to drive fasteners such as a nail by an electric impact tool, however, substantial impact forces are necessary.
One type of prior art electric impact tool directly couples the driver to the source of electricity. This tool does not generate sufficient driving forces for large fasteners since the necessary structure to develop a sufficient force in a short span of time is too bulky or heavy for most electric tools, particularly, portable hand-held tools.
A second type of electric tool employs one or more rotational energy devices such as a flywheel. The flywheel is constantly rotated by an electrical motor and once it is desired to power the driver through a driving stroke, the flywheel is mechanically coupled to the driver. Upon completion of the driving stroke, the flywheel is uncoupled from the driver.
This second type of tool draws energy from the flywheel for only a brief period of time allowing the flywheel to regain lost energy in preparation for the next driving stroke. In this manner, a constant source of substantial driving power is available while employing the same source of electrical energy as the first type of tool.
One disadvantage of this latter type of impact tool is that several mechanical components are necessary to couple the flywheel to the driver. An example of a tool employing elaborate structure to couple the flywheel to the driver is illustrated in U.S. Pat. No. 1,823,644.
Further, some tools use a complex structure including springs and cams mechanically operated by hand levers. An example of this type of tool is illustrated in U.S. Pat. No. 2,378,131.
A further type of tool employs two high speed rotating flywheels one of which is moved into engagement with driver capturing the driver between the two flywheels. Such a device requires two motors, one for each rotating flywheel, in addition to requiring additional mechanical structure to maintain the movable flywheel in a stable position while the driver is in a static position. Additional structure is also required to move the flywheel into engagement with the driver.